Apparatus for melting powdered material by means of a flame elevated temperature



June 22, 1965 A. VUNDERINK 3,190,727 APPARATUS FOR MELTING POWDERED MATERIAL BY MEANS OF A FLAME ELEVATED TEMPERATURE Filed May 10. 1961 ,{TE vu/v R/ INVEN TOR.

United States Patent 3,190,727 APPARATUS FOR MELTING POWDERED MATE- RIAL BY MEANS OF A FLAME ELEVATED TEMPERATURE Ate Vunderink, Bussum, Netherlands, assignor to Ronette Piezo Electrische Industrie N.V., Amsterdam, Netherlands, a corporation of the Netherlands Filed May 10, 1961, Ser. No. 109,067 Claims priority, application Netherlands, June 25, 1960, 253,106/ 60 4 Claims. (Cl. 23-273) The present invention relates to an apparatus for melting powdered material by means of a flame of elevated temperature and for precipitating said molten material, including a burner comprising two concentric tubes, the outermost of which is connected to a source of combustible gas and the innermost of which is connected to a source of oxygen, a powder dosing device communicating with the innermost tube and a catching surface movable relative to the burner in the longitudinal direction thereof, said catching surface being movable away from the burner by a driving means at such a rate that the distance between the mouth of the burner and the latest material precipitated on said catching surface remains constant. I

Apparatuses of this type have long since been known.

The object of the method to be carried out by means of such apparatuses is to form a pear or rod-shaped body from powdered material having a high melting point, by melting the particles of the powder and by precipitating said molten particles on a catching surface, said pear or rod-shaped body consisting of a monocrystal of the desired material or of a polycrystalline form of said material, in Which the crystallites have a specific orientation.

Said method may be used for example for the manufacture of synthetic corundum and spinel.

One of the most important conditions that is to be satisfied if the method is to proceed satisfactorily, is that the rate of growth of the body to be formed is kept constant very accurately. Said rate of growth especially depends on the amount of powder supplied to the flame and is furthermore influenced by changes, if any, in the distance between the burner mouth and the surface on which the molten particles precipitate.

The object of this invention is to provide an apparatus which very favourably compares with the known apparatuses as regards the fulfilment of the conditions just mentioned.

To achievev this end the apparatus according to the invention is characterized in that the powder dosing device comprises a generally closed hollow body, whose interior is divided by a horizontal porous powder-carrying plate into a lower space which is in direct communication with the source of oxygen and an upper space which communicates both with the inner burner tube and with a powder reservoir.

According to another feature the apparatus according to the invention may comprise a space with which the source of oxygen, the innermost burner tube and the upper space of the hollow body respectively are in direct communication.

According to still another feature of the apparatus according to the invention the innermost burner tube downwardly extends through the wall of the hollow body into the upper space of said body, a thinner tube open at the upper side extending into the open lower side of said burner tube, the lower side of said thinner tube communicating with the source of oxygen.

According to a further feature of the apparatus, according to the invention, it comprises an impeller which can set the powder particles moving to a relatively slight extent both relative to each other and relative to the porous powder-carrying plate and the wall of the hollow body respectively.

An apparatus provided with -a photo-electric control device which receives light emitted by the most recently precipitated molten material and which in dependence on the light intensity produces a control current, may be so designed according to the invention, that said control current influences the position of a distributing means provided in the conduits leading from the source of oxygen to the innermost burner tube and to the space beneath the porous powder-carrying plate respectively, the driving means moving the catching surface with a constant speed. s

For elucidating the invention some embodiments of the apparatus will be described with reference to the accompanying drawings, in which:

FIG. 1 is a schematic showing of an embodiment according to the invention, the flame to be produced being directed upwardly;

FIG. 2 is a schematic showing of a portion of an apparatus as shown in FIG. 1, however, in an alternative embodiment;

FIG. 3 is a schematic showing of an apparatus similar to the one shown in FIG. 1, in this embodiment, however, the flame is directed in a downward direction;

FIG. 4 is a schematic showing of a portion of the apparatus shown in FIG. 1, which, however, is provided with an additional impeller means for keeping the powdered material in motion.

The burner shown in FIG. 1 comprises an innertube 1 and an outertube 2 arranged concentrically in respect to each other. A supply tube 3 coming from a device for supplying a combustible gas is connected to the outer tube 2. Said conduit 3 contains a regulating valve 4. A conduit 5 connected to the source of oxygen (not shown) and provided with a regulating valve 7 branches into a conduit 40 and a conduit 9. The conduit 40 leads via a regulating valve 8 to a chamber 6,.WhiCl1 is in direct communication with the innertube 1. -The conduit 9 leads via a regulating valve 10 to the powder dosing device to be described hereinafter. The regulating valves 8 and 10 may be moved by a common actuating mechanism 28 in such a manner that if the one regulating valve is opened further, the other regulating valve is closed further and conversely. Regulating valves 8 and .10 together therefore always divide between themselves the stream of oxygen admitted by regulating valve 7.

The powder dosing device is formed by a vessel 11. Said vessel 11 is open at the upperside and is connected with the chamber 6 by means of a sleeve 12. The space in vessel 11 is divided into an upper space 13 and a lower space 1 4- by a powder-carrying plate 15. Said carrying plate 15 is porous and may consist, for example, of sintered glass. The conduit 9 communicates with the lower space 14-. By means of a supply tube 16 provided with a valve 17 the upper space 16 is connected to a powder reservoir (not shown). The flame produced by the burner is schematically shown at 18. Said flame entrains particles which may precipitate on a catching surface 19. Said catching surface 19 is secured to a driving means schematically shown as consisting of a toothed rack 20 which by means of a rotatable pinion 21 can be moved vertically up and down. The material precipitated on the catching surface 19 in the form of a gradually growing rod is shown at 2'2. Beside the place where the molten material precipitates an optical system has been positioned which is schematically designated by the numeral 23.

Said optical system 23 is so arranged and directed as to receive the light emitted by the molten material that has just precipitated. Said light is concentrated by the optical system 23 into a bundle which falls on a photo-electric cell 24. The electric current produced by the photo-electric cell 24 is passed by leads 25 to an electric amplifier 26. The currents amplified by said amplifier 26 are passed by leads 27 to the mechanism 28 for moving the regulating valves Sand 10.

The operation of the apparatus is as follows:

Via supply line 16 and valve 17, powder may be supplied to upper space 13 of vessel 11 so that continuously a layer of powder is present on the powder-carrying plate 15. Combustible gas enters the apparatus via conduit 13, the regulating valve 4 being entirely or partly open, said gas subsequently flowing upwardly through the outer tube 2. Oxygen is fed to the apparatus through conduit 5, the regulating valve 7 being entirely or partly opened and the regulating valves 8 and 10 each occupying a specific distributing position. The oxygen therefore will be led in the first place into the chamber 6 and in the second place will enter the lower space 14 of vessel 11. From chamber 6 oxygen may escape in upward direction through the inner tube 1. In chamber 6 a Weak flow in upward direction results therefore. The oxygen which has entered the lower .space 14 will force its way upwards through the pores of the powder-carrying plate 15 and through the powder lying on said plate. It is known that under such conditions the powder will behave as if it were a boiling liquid. Above the layer of powder, a clear upper boundary of which cannot be indicated for that matter, the powder is in a floating state. The floating powder together with the stream of oxygen carrying the powder is fed upwardly towards the chamber 6 as a result of the earlier mentioned flow of oxygen which is upwardly directed. The effect therefore is that oxygen mixed with an amount of very finely divided powder flows through the inner tube 1. The total amount of oxygen supplied can be regulated by the position of the regulating valve 7. Said total amount of oxygen is regulated in dependence of the amount of combustible gas which in its turn can be regulated by means of the regulating valve 4.

The powder content of the stream of oxygen can be very accurately regulated by means of regulating valves 8 and 10. An increase in the amount of oxygen flowing through valve 10 for example-which is of necessity attended by an equally large decrease in the amount of oxygen flowing through regulating valve 8has for its result that the larger amount of oxygen flowing through the porous powder-carrying plate 15 will entrain more powder to chamber 6, The result, therefore, is, that the same amount of oxygen flows through the inner tube 1, but that the stream of oxygen now entrains more powder.

As the material precipitates, initially on the catching surface 19 and afterwards on the material which has already precipitated thereon, the toothed rack 20 is gradually drawn upwardly owing to the rotation of the pinion 21 according to the arrow 29. As already stated before it is the intention that the distance between the burner mouth and the place of crystal growth remains very accurately constant. Now this is achieved 'by means of an optical device 23 in cooperation with a photo-electric cell 24.

The optical device is so directed that an image is obtained of the most recently precipitated material as well as of the tip of the flame. Seeing that such a flame emits relatively little light the total light intensity will be determined substantially exclusively by the growing crystal body. The intensity of the light received therefore is slight if the photoelectric cell 24 does not receive light from the place of growth of the crystal body and the intensity is large if said light is received. Now this latter case presents itself if the crystal growth should take place slightly too rapidly.

In said case the rate of growth should be slightly diminished which may be achieved by introducing less powder into the flame. This is effected because the increased intensity of the light received by the photo-electric cell 24 produces an electric current which after being amplified by the amplifier 26 causes the actuating mechanism 28 to move in such a manner that a larger amount of oxygen flows through the regulating valve 8 and a smaller amount flows through the regulating valve 10, the sum of the two amounts remaining always equal, so that if the total feed of oxygen remains constant the supply of powder to the flame will decrease. This will result therefore in a decrease in the rate of growth of the crystal, so that the place of growth will move upwardly relative to the burner mouth, until the image formed by the optical system 23 has again the correct configuration. This control of the rate of growth by controlling the dosing of powder is exceedingly accurate, so accurate in fact that the object contemplated is fully achieved thereby. As a result it is no longer necessary to employ the method that has hereto been used and according to which differences in the rate of growth were compensated for by temporarily moving the catching surface upwardly more rapidly or more slowly. These conventional devices for varying the speed of movement of the catching surface were relatively complicated and not very accurate.

In the present apparatus the catching surface is moved upwardly with a constant speed and the rate of growth itself is redressed by means of the dosing of powder.

FIG. 2 shows a slightly amended embodiment. In said embodiment the inner tube 30 extends downwardly into the vessel 11. The oxygen conduit 5 after the regulating valve 7 branches into a conduit 9 including a regulating valve 10 and into a conduit 31 including a regulating valve 32. The regulating valves 10 and 32 are again so coupled that together they determine the division between conduits 9 and 31 of the stream of oxygen which the regulating valve 7 allows to pass.

In describing this figure and the following figures corresponding elements will be designated by the same reference numerals.

The conduit 31 is passed through a wall of the vessel 1 and extends upwardly into the downwardly extending inner tube 30. If an oxygen stream flows through conduit 31 via regulating valve 32 into the wider inner tube 30 this will result in a sucking action in known manner, which makes itself felt at the open lower end of the inner tube 30. Seeing that the vessel 11 in the same manner as described hereinbefore is filled with a very finely divided and floating powder, powder will be sucked in by the open lower side of the inner tube 30 and said powder will thus find its way into the flame. For simplicitys sake the regulating valves 42 and 32 are shown as manually operated valves in this figure. It will be clear, however, that also in this embodiment valves can be used of a type corresponding with the regulating valves 8 and 10 of FIG. 1, which admit of being operated by an optical-electrical control device.

FIG. 3 shows an embodiment in which the flame is directed downwardly and in which therefore the catching surface is moved in downward direction away from the burner mouth. This embodiment largely corresponds with the embodiment according to FIG. 1. However, the inner tube 33 extends upwardly into the vessel 34, the upper portion 35 of which is formed as a mixing chamber. The oxygen directlysupplied to said chamber 35 enters same through a branch 36 of conduit 5. Upon the entrance of said oxygen into the inner tube 33 some suction will result again which will entrain part of the floating powder in vessel 34 down through the inner tube 33 into the flame 18.

The apparatuses described hereinbefore may be provided with an additional member which in some cases yields an improvement, for the circumstance may present itself, notably in the case of certain kinds of powder that the oxygen passing through the powder-carrying plate will form fine grains in the powder on the plate. The powder therefore, as it were, will be given a certain structure, which has for its result that the powder can less readily Such an impeller member may be realized in many manners. According to the embodiment as shown in FIG. 4 said friction is overcome because above the powder-carrying plate an impeller mechanism is arranged which keeps the powder in a continuous slow motion. Said impeller mechanism comprises a set of blades 38 mounted on a vertical shaft 39 which shaft is slowly rotated by a driving mechanism 41.

I claim:

1. In apparatus for melting powdered material by means of a flame of elevated temperature and for precipitating said molten material in the form of a rod, including a burner comprising two concentric tubes, means to supply combustible gas to the outer of said tubes, a catching surface adjacent and in vertical axial alignment with said burner for precipitated material, means to move said catching surface away from the burner in a vertical direction, powderdosing means including a closed vessel having a perforate bottom surface, means to supply powder to the interior of said vessel, means to supply oxygen under pressure to the bottom of said supply of powder below said perforate surface in the vessel to create a fluidized bed of powder, conduit means connecting an upper region of said fluidized bed of powder with said inner burner tube to inject said powder into said flame, and a common oxygen source having two outlet pipes and proportioning valve means, one of said outlet pipes being in communication with said inner burner tube above the fluidized bed of powder, the outer outlet pipe being in communication with the under side of the fluidized bed, said proportioning valve means being adjustable to simultaneously control the rate of flow of oxygen to one pipe inversely to the rate of flow to the other pipe, and photo electric means responsive to material precipitated on said catching surface to regulate said proportioning valve means.

2. The invention as defined in claim 1, wherein the upper end of said vessel terminates in said conduit means in communication with said inner burner tube, the wall of said conduit means being provided with an opening, said means to supply oxygen to said inner tube also being in communication with said opening.

3. The invention as defined in claim 1, wherein said inner burner tube projects downwardly into the fluidized bed of powder, and said means to supply oxygen to the inner tube includes a third tube concentrically positioned Within and projecting upwardly into said inner tube, said third tube being of substantially less diameter than the inner tube.

4. The invention as defined in claim 1 wherein impeller means is provided adjacent said perforate surface to induce motion to the powder particles.

References Cited by the Examiner UNITED STATES PATENTS 1,960,615 5/34 Baker. 2,462,995 3/49 Ritzmann. 2,472,951 6/49 Klinke 266-23 2,692,456 10/ 5 4 Dauncey. 2,737,997 3/56 Himmelheber et a1. 2,792,287 5/57 Moore et a]. 23-202 2,874,763 2/59 Hobbs 250--2l8 2,905,989 9/59 Black 22-57.3 2,924,489 2/60 Beckman.

FOREIGN PATENTS 243,251 11/25 Great Britain.

710,306 6/54 Great Britain. 1,260,884 6/60 France.

NORMAN YUDKOFF, Primary Examiner.

ANTHONY SCIAMANNA, MAURICE A. BRINDISI,

Examiners. 

1. IN APPARATUS FOR MELTING POWDERED MATERIAL BY MEANS OF A FLAME OF ELEVATED TEMPERATURE AND FOR PRECIPITATING SAID MOLTEN MATERIAL IN THE FORM OF A ROD, INCLUDING A BURNER COMPRISING TWO CONCENTRIC TUBES, MEANS TO SUPPLY COMBUSTIBLE GAS TO THE OUTER OF SAID TUBES, A CATCHING SURFACE ADJACENT AND IN VERTICAL AXIAL ALIGNMENT WITH SAID BURNER FOR PRECIPITATED MATERIAL, MEANS TO MOVE SAID CATCHING SURFACE AWAY FROM THE BURNER IN A VERTICAL DIRECTION, POWDER DOSING MEANS INCLUDING A CLOSED VESSEL HAVING A PERFORATE BOTTOM SURFACE, MEANS TO SUPPLY POWDER TO THE INTERIOR OF SAID VESSEL, MEANS TO SUPPLY OXYGEN UNDER PRESSURE TO THE BOTTOM OF SAID SUPPLY OF POWDER BELOW SAID PERFORATE SURFACE IN THE VESSEL TO CREATE A FLUIDIZED BED OF POWDER, CONDUIT MEANS CONNECTING AN UPPER REGION OF SAID FLUIDIZED BED OF POWDER WITH SAID INNER BURNER TUBE TO INJECT SAID POWDER INTO SAID FLAME, AND A COMMON OXYGEN SOURCE HAVING TWO OUTLET PIPES AND PROPORTIONING VALVE MEANS, ONE OF SAID OUTLET PIPES BEING IN COMMUNICATION WITH SAID INNER BURNER TUEBE ABOVE THE FLUIDIZED BED OF POWDER, THE OUTER OUTLET PIPE BEING IN COMMUNICATION WITH THE UNDER SIDE OF THE FLUIDIZED BED, 